Swim fins are utilized in, e.g., snorkelling and diving, in freediving as well as scuba diving, to convert the principally vertical leg kick of the legs into an improved propulsion and thereby the speed of the body in the water. The swim fins are usually manufactured entirely or partly of rubber and embrace a shoe and a blade. When using swim fins, the blade usually flexes in the opposite direction to the one that the leg moves because of the resistance of the water, which decreases the performance of the swim fin. By the shoe and blade of the swim fin being formed integrally, turbulence also arises in the vicinity of the transition between the foot and the blade, which also is a disadvantage in respect of the performance of the swim fin.
An additional disadvantage of today's fins is that the angle between the foot portion including the attached blade and the direction of travel (as defined in FIG. 6) is small, which impairs the performance of the swim fin. In addition, the blade is usually not shaped as a hydrofoil blade/fin, which further impairs the performance of the swim fin.
Yet a disadvantage of today's swim fins is that it is only possible to swim forward when executing a conventional leg kick. In certain types of diving, e.g., in diving in narrow spaces, such as in caves or inside wrecks, wherein the diver has difficulties in turning around, it would be desirable to be able to convert the usually forwardly acting force of the kick of the leg to a backwardly acting force, i.e., a reverse motion. Also upon ascent, it may in certain cases be desirable with a reverse motion to slow down the ascension speed and thereby decreasing the risk of decompression sickness.
By U.S. Pat. No. 4,934,971, a swim fin is known the blade of which is limitedly pivotally attached to arms, which arms are attached to a foot portion with a relatively large angle between the foot portion and the direction of travel, and the blade of which is in the form of a fin.
By U.S. Pat. No. 5,536,190, a swim fin is known comprising a plurality of hydrofoil blades the angle of attack of which is automatically self-adjusting by the utilization of a negative feedback via one or more hydrodynamic control surfaces.